568 A NATURALIST ON THE "CHALLENGER." 



sticky gelatinous strings, which it forms for the purpose. In 

 the centre of the nest are deposited the eggs. 



The Weed is much encrusted by a Bryozoon (Membranipora), 

 which makes conspicuous white patches upon its surface. 

 Numbers of the detached air-vessels of the Weed are to be seen 

 floating about amongst the living Weed-beds, coated entirely 

 with the white Membranipora, and they look at first like small 

 globular Pelagic animals. 



All the inhabitants of the Gulf Weed are most remarkably 

 coloured, for purposes of protection and concealment, exactly like 

 the Weed itself. The Shrimps and Crabs which swarm in the 

 Weed are of exactly the same shade of yellow as the Weed, and 

 have white markings upon their bodies to represent the patches of 

 Membmnipora. The largest shrimp occurring has a dark-brown 

 colour with brilliant- white sharply defined areas upon its surface, 

 thus closely resembling the older darker-coloured pieces of Weed, 

 which are also most thickly covered with Membranipora. 



The small fish (Antennarius) is in the same way coloured 

 Weed-colour with white spots. Even a Planarian worm, which 

 lives in the Weed, is similarly yellow-coloured, and also a Mollusc 

 (Scyllcea pelagica). The white patches on some of the Crabs, no 

 doubt, represent also, to some extent, the white shells of 

 Barnacles, though these are not very abundant in the Weed. A 

 small Crab, Nautilograpsns minutus, which varies very much in 

 colour, very abundant amongst the Weed, is constantly to be 

 found also in large numbers hanging on to floating logs and 

 similar objects elsewhere, and in these cases the white patches 

 on its body correspond closely with the barnacles by which the 

 logs are covered. These little crabs vary extremely in the 

 arrangement and forms of the white patterns on their backs, 

 and we found a number of them once (I believe of the same 

 species) which were clinging to the floats of the blue-shelled 

 Pelagic Mollusc lanthina, and these were all coloured, for con- 

 cealment, of a corresponding blue. 



Pelagic animals generally seem to be either colourless or 

 specially coloured, with a view to protection from enemies both 

 above and below the surface of the water. Probably the blue 

 colour of lanthina and Velella is protective as resembling that 



